Re: [PATCH 2/5] vrange: Add purged page detection on setting memory non-volatile

[KOSAKI Motohiro <kosaki.motohiro@gmail.com>]

On Fri, Mar 21, 2014 at 2:17 PM, John Stultz <john.stultz@linaro.org> wrote:
> Users of volatile ranges will need to know if memory was discarded.
> This patch adds the purged state tracking required to inform userland
> when it marks memory as non-volatile that some memory in that range
> was purged and needs to be regenerated.
>
> This simplified implementation which uses some of the logic from
> Minchan's earlier efforts, so credit to Minchan for his work.
>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Android Kernel Team <kernel-team@android.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Robert Love <rlove@google.com>
> Cc: Mel Gorman <mel@csn.ul.ie>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Dave Hansen <dave@sr71.net>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Dmitry Adamushko <dmitry.adamushko@gmail.com>
> Cc: Neil Brown <neilb@suse.de>
> Cc: Andrea Arcangeli <aarcange@redhat.com>
> Cc: Mike Hommey <mh@glandium.org>
> Cc: Taras Glek <tglek@mozilla.com>
> Cc: Jan Kara <jack@suse.cz>
> Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
> Cc: Michel Lespinasse <walken@google.com>
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: linux-mm@kvack.org <linux-mm@kvack.org>
> Signed-off-by: John Stultz <john.stultz@linaro.org>
> ---
>  include/linux/swap.h    | 15 ++++++++--
>  include/linux/swapops.h | 10 +++++++
>  include/linux/vrange.h  |  3 ++
>  mm/vrange.c             | 75 +++++++++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 101 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 46ba0c6..18c12f9 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -70,8 +70,19 @@ static inline int current_is_kswapd(void)
>  #define SWP_HWPOISON_NUM 0
>  #endif
>
> -#define MAX_SWAPFILES \
> -       ((1 << MAX_SWAPFILES_SHIFT) - SWP_MIGRATION_NUM - SWP_HWPOISON_NUM)
> +
> +/*
> + * Purged volatile range pages
> + */
> +#define SWP_VRANGE_PURGED_NUM 1
> +#define SWP_VRANGE_PURGED (MAX_SWAPFILES + SWP_HWPOISON_NUM + SWP_MIGRATION_NUM)
> +
> +
> +#define MAX_SWAPFILES ((1 << MAX_SWAPFILES_SHIFT)      \
> +                               - SWP_MIGRATION_NUM     \
> +                               - SWP_HWPOISON_NUM      \
> +                               - SWP_VRANGE_PURGED_NUM \
> +                       )

This change hwpoison and migration tag number. maybe ok, maybe not.
I'd suggest to use younger number than hwpoison.
(That's why hwpoison uses younger number than migration)